Rotatable dielectric slab phase-shifter for waveguide



Aug. 23, 1955 P. J. ALLEN 2,716,221

ROTATABLE DIELECTRIC SLAB PHASE-SHIFTER FDR WAVEGUIDE Filed Sept.25/1950 I MOTOR %:+a-=r: ""A

INVENTOR PHILIP J. ALLEN United States Patent ROTATABL-E DIELECTRIC SLABPHASE-SHIF'IER FOR WAVEGUIDE Philip J. Allen, Washington, D. C.Application September 25, 1950, Serial No. 186,623

4 Claims. (Cl. 333-31) (Granted under Title 35, U. S. Code (1952), see.266) This invention relates to phase shifting apparatus for use .in highfrequency transmission systems utilizing hollow waveguides as thetransmission means.

More particularly, the present invention relates to phase shiftingapparatus for use in hollow waveguides where the degree of phase shiftmay be simply and quickly varied.

It is known in the prior art that varying the dielectric constant of themedium in which an electromagnetic wave is travelling will vary thevelocity of propagation of the wave travelling therein. This change invelocity causes a change in phase of the wave.

Hollow waveguides are utilized as a conduit for electromagnetic energyand placing a piece of low-loss dielectric material Within a waveguidewill shift the phase of the waves travelling therein for the reasonsjust described.

The present invention utilizes a low-loss dielectric material to varythe phase shift of the electromagnetic waves within a hollow waveguidein a novel and expeditious way.

The degree to which the phaseof the energy within a hollow waveguide isshifted by a dielectric material placed therein has been found to dependupon the volume of material within the waveguide cavity, the dielectricconstantof the material, and the electric field intensity in thevicinity thereof. Thus, if a given amount of dielectric material is tobe placed in a waveguide, inserting it in the vicinity of maximumelectric field intensity will cause a maximum apparent phase shift tooccur within the waveguide. Conversely, placing a given amount ofdielectric material in the portions of the cavity having the leastelectric field intensity will cause a minimum amount of phase shift.

Accordingly, the present invention utilizes one or more dielectricmembersrotatably mounted within the confines of'a hollow waveguide sothat the members are positioned in-areas of varying electric fieldintensity as the members are rotated. Each member rotates about an axiswhich runs generally parallel to the length of the waveguide.

In one embodiment, the axis of rotation passes through each member. Thedistance from the axis of rotation to theouter surfaces of the membersis varied about the axis so that rotating the members varies therelative position between the non-uniform electric field and thedielectric member thereby varying the phase shift.

In another embodimentthe members are made of material of varyingdielectric constant so that rotating the member will cause a variationin phase shift due to the change in relative position between theelectric field and the non-uniform dielectric 'member.

'In a third embodiment of the present invention, the axis of rotation islocated outside of the dielectric member so that rotation of said memberabout the axis places the member in electric fields of varyingintensity.

:2 energy fed to the antenna elements. By driving the dielectric plateat a high rate of speed, the phase shift of the waveguide energy isquickly varied with ease and simplicity. This was not readily possiblewith the cumbersome prior art phase shifting devices.

Accordingly one object of the present invention is to provide a noveland simple phase shifting device for use in hollow waveguide systems.

Another object of the present invention is to provide a novel and simplephase shifting device for use in hollow waveguide systems for quicklyand continuously varying the phase shift of the energy within thewaveguide.

These and other objects of the present invention will become apparentfrom the specification and drawings wherein:

Figure l is a cross-sectional view of a hollow waveguide showing thephase shifting device forming one embodiment of the present inventionlocated therein.

Figure 2 is a cross-sectional view of Figure 1 along section line 22.

Figure 3 is a cross-sectional view of the phase shifting apparatuswithin a hollow waveguide showing the dielectric members in a differentposition from that of Figure 1.

Figure 4 is a View taken along section line 4-4 of Figure 2 includinglines representing the electric field intensity across the waveguidecavity.

Figure 5 shows the curves of phaseshift versus degrees of plate rotationfor 'two relative positions of the dielectric plates shown in Figures1-4.

Figure 6 is a second embodiment of the present invention where thedielectric constant of the --dielectric member is varied.

Figure 7 is a third embodiment of the present invention.

Referring now to the drawings Figures 1 "to 4, Where like referencecharacters denote identical elements, the cavity of a hollow waveguide 1contains two dielectric members 2 and 3. A low-loss dielectric materialsuch as polystyrene is preferred for the dielectric members. The'members 23 are mounted on a shaft 4 so as to be rotatable togetherabout an axis AA'which runs lengthwise of the waveguide (i. e. generallyparallel "to the waveguide axis). The cross-sectional area of themembers 23 in a plane perpendicular to the axis of rotation AA is madeoblong in shape for reasons which will be "hereinafter explained in moredetail.

To simplify the drawings, the bearings for shaft-4 have been omitted.

The electric field lines within a rectangular waveguide run parallel tothe short dimension of the rectangular waveguide 1 for the TE 1,0 modeas shown in Figure 4 (the density of lines represent the density of theelectric field). When dielectric member 3 is in the horizontal positionshown by the solid lines in Figure 4, minimum phase shift occurs becausethe average electric field intensity in the space occupied by member 3is a minimum. When member 3 has the vertical position shown by thedotted lines in Figure 4, since all of the dielectric material is in theregion of greatest intensity, maximum phase shift will result. If member3 is rotated as by motor 5 which imparts motion thereto through itsshaft 4, then member 3 will cause a periodic variation inyphase shiftresembling curve b in Figure 5. As there shown, one revolution therecauses two cycles of phase shift variation.

If the cross section of the homogeneous dielectric member 3 werecircular rather than rectangular, and the axis of rotation was locatedat the center thereof, then rotation of the member would cause novariation in phase shift since the average field intensity in the spaceoccupied by member 3 remains constant.

From what has been said, it is apparent that a rectangular cross sectionis not necessary to the operation of the embodiment of Figures 1-4.However, it is imsections 88'.

3 portant that the distance from the axis of rotation to the surface ofthe dielectric member vary about the axis as measured in a planeperpendicular to the axis.

The cross section is made oblong in shape to obtain large phase shiftvariations in the embodiment just described.

From Figure 5, it can be seen that the phase shift variation follows thegeneral outlines of a sinusoidal wave when the homogeneous rectangularshaped dielectric member was used.

For best results with this embodiment, the axis of rotation of thedielectric member 3 should be in the vicinity, of maximum electric fieldintensity and in the center section C-C of the wave guide as shown inFigure 4.

Two dielectric members 23 which are rotatable together are provided inorder that the amplitude of the phase shift variation may be simply andconveniently controlled. Each dielectric member 2,.3, causes a phaseshift variation and the net effect of the two members is the sum of theindividual eifects of the dielectric members. That is, the dielectricmembers are serially mounted with respect to the electromagnetic energybeing propagated in' the waveguide and hence as in the common seriesrelationship the net efiect is the sum of the individual effects.

When members 23 are placed at right angles to each other, on shaft 4,the variation'in average electric field intensity in the space occupiedby dielectric member 23 throughout a given revolution is substantiallyzero so that there is little or no variation in phase shift with therotation of the dielectric members as shown by curve a in Figure 5.

As members 23 are gradually brought into coincidence (i. e. as angle 0approaches zero), the amplitude variation of the phase shift curveincreases. Curve b in Figure 5 represents the phase shift variation whenthe dielectric members have the position shown in Figure 3,

Motor shaft 4 may be made of a metallic material without appreciablyaffecting the field intensity or the losses in the waveguide as long asthe cross section of shaft 4 is small relative to that of the waveguide1.

Shaft 4 extends through openings in dielectric members 23 and therebycauses simultaneous rotation of the dielectric members. The closeness ofthe fit between one of the dielectric members and shaft 4 is made suchthat the latter member may be initially positioned rela tive to theshaft 4 in order to vary the relative angle 9 between the dielectricmembers, but the fit is sufficiently close that the member will not slipas the shaft 4 is rotated.

Other suitable coupling means may of course be utilized.

In Figure 6 is shown another embodiment of the present invention,wherein the dielectric member is nonhomogeneous and cylindrical in shaperather than being homogeneous and fiat as in the embodiment of Figuresli-4. The cylindrical member there shown comprises two arcuate sections8-8 made of one kind of dielectric material, and a center section 7 madeof a dielectric material having a different dielectric constant than theIf section 7 has a dielectric constant which is greater than that ofsection 8-8, and the center section'is generally parallel to theelectric field lines, maximum phase shift will result. When the centersection 7 runs generally perpendicular to the electric field lines,minimum phase shift occurs.

Two angularly disposed similar cylindrical members may be used in themanner described in connection with the embodiment of Figures l4 toprovide a control over the amplitude of phase shift variation.

This embodiment has the disadvantage that it causes more impedancemismatch than the embodiment of Figures 1-4 since it displaces a greatercross-sectional area of the waveguide. Also smaller phase shift ampliiiitude variations are obtained with the embodiment of Figure 6. A

Figure 7 is a third embodiment of the present invention wherein the axisof rotation is located along one side of the waveguide cavity and isdisplaced from the dielectric member.

Radially of the axis of rotation are located dielectric members 2' and 3which are angularly displaced from each other along the axis as aredielectric members 23 in Figure 2., Members 2 and 3' are shown similarin shape to members 23 but of course may have any suitable shapedepending on the phase shift variation desired.

The dielectric members 23' are connected with shaft 4 by dielectric ribmembers 9'10. As the members are rotated, they are placed in electricfield of varying intensity. When the dielectric members are in thecenter section of the waveguide they produce the greatest phase shiftsince the intensity of the electric field is there maximum for the TE1,0 mode.

As the relative position of members 2' and 3' is varied from the rightangle relationship shown in Figure 7,

the amplitude of the net phase shift variation increases for reasonsapparent from the explanation of the operation of the other embodiments.u

Although the present invention has been only applied to a rectangularwaveguide operating in the TE 1,0 mode, it should be understood that theinvention herein disclosed is also applicable to waveguides of othermodes of electric field distribution.

It should be understood that many modifications may be made of thespecific embodiments herein disclosed without deviating from the scopeof the present invention.

The invention described herein maybe manufactured and used by or for theGovernment of the United States I of America for governmental purposeswithout the payment of any royalties thereon or therefor;

What is claimed is:

l. A phase shifting device for use in hollow waveguide electromagneticenergy transmission systems comprising first and second dielectricmembers rotatably mounted for rotation together within a hollowwaveguide about an axis running within and lengthwise of said waveguide,the distance from said axis to the surface of said members varying aboutsaid axis, said members being displaced from each other along said axisand lying serially in the path of the electromagnetic energy beingpropagated in said waveguide, the angular relation between said membersbeing adjustable whereby the amplitude of the phase shift variation maybe readily varied.

' 2. A phase shifting device for use in hollow waveguide electromagneticenergy transmission systems comprising first and second dielectricmembers, means for rotating said members together within a hollowwaveguide through electric fields of varying intensity about an axislocated within and lengthwise of said waveguide, said members beingdisplaced from each other along said axis and lying serially in the pathof the electromagnetic energy being propagated in said waveguide, thedistance from said axis to the surface of said members varying aboutsaid axis, the angular relation between said members being adjustablewhereby the amplitude of the phase shift variation may be readilyvaried.

3. A phase shifting device for use in hollow waveguide electromagneticenergy transmission systems comprising first and second dielectricmembers, means for rotating said members within a hollow waveguidethrough electric fields of varying intensity about a given axis locatedwithin said waveguide in the vicinity of maximum electric fieldintensity, each of said members being dielectrically unsymmetrical aboutsaid axis, said members being displaced from each other along said axisand lying serially in the path of the electromagnetic energy beingpropagated in said waveguide, the angular relation between said membersbeing adjustable whereby the amplitude of the phase shift variation maybe readily varied.

4. A phase shifting apparatus comprising a section of waveguide for thetransmission of electromagnetic energy, a pair of dielectric phaseshifting members disposed in said section of waveguide, means forrotating said members about an axis located within said waveguide in theregion of maximum electric field intensity, said members beinglongitudinally displaced from each other along said axis and lyingserially in the path of the electromagnetic energy being propagated insaid waveguide, each of said members being dielectrically unsymmetricalabout said axis, and means for changing the relative angularrelationship between said members to provide a phase shift variation ofvariable amplitude.

References Cited in the file of this patent UNITED STATES PATENTS KingApr. 16, 1940 Johnson et al Dec. 30, 1947 Fox Mar. 23, 1948 Revercomb eta1. Oct. 4, 1949 Marshall Jan. 24, 1950 Tyrrell Mar. 27, 1951 WhiteSept. 11, 1951 Hansen July 8, 1952 FOREIGN PATENTS Great Britain June28, 1948

